Packaging

ABSTRACT

The present invention provides a wall for a package, which wall comprises, or includes a layer comprising, a composition comprising a polymer and capable of scavenging oxygen through the metal-catalysed oxidation of an oxidisable organic component thereof. The oxidisable organic component is preferably itself a polymer, and may be the only polymer in the composition. Preferred compositions include a blend of 96% polyethylene terephthalate and 4% poly (m-xylyleneadipamide) containing 200 ppm cobalt as catalyst, with good permeance-versus-time performance (3) when formed into a bottle.

[0001] The present invention relates to packaging, especially packagingof oxygen-sensitive materials, most especially of foods and beverages.

[0002] Packaging, whether rigid, semi-rigid, flexible, lidded, orcollapsible, or a combination of these, serves not merely to contain thematerial being packaged but, depending on the nature of the material, toprevent ingress of harmful substances from the environment. Oxygen fromthe atmosphere has long been regarded as one of the most harmfulsubstances for many packaged materials, especially foodstuffs.

[0003] Packaging made exclusively of glass or metal can provide anextremely good barrier both to egress of all substances from the package(especially water and carbon dioxide) and to ingress of all substancesfrom the environment. Packaging made of polymers in whole or in partgenerally performs far less well in both these respects. This hasrestricted for many years the use of polymers in packaging, despite thegreat advantages of polymers. These advantages derive from the diversityof polymers themselves in mechanical, thermal, and optical propertiesand from the diversity and adaptability of fabrication techniques forpolymers, allowing flexible bags, rigid containers, and clinging filmsto be made, the package wall being homogeneous, laminated, or coated.Compared with glass and metal packages, polymer packages are generallylight and compared with glass are generally less breakable. There arealso cost advantages with some polymers.

[0004] Polyethylene terephthalate is a major packaging polymer, usedparticularly for bottles for carbonated beverages. It is over twentytimes less permeable than polypropylene while still having a practicallysignificant permeability. There are extremely impermeable polymers suchas copolymers of ethylene and vinyl alcohol, of vinylidene chloride andvinyl chloride, and of m-xylylenediamine and adipic acid (“MXD6”); butfor practical or cost reasons these tend to be used as thin layers on orbetween polyethylene terephthalate or (in the case of-MXD6) for blendingwith polyethylene terephthalate, in low percent quantities, stillleaving practically significant permeability. For instance, orientedblends of polyethylene terephthalate (96%) and MXD6 (4%) are about 70%as permeable as polyethylene terephthalate. Chemical Abstracts, 1984,volume 100, abstract 100: 193165x, being an abstract of Japanesepublished patent application 58 160344, gives some information on theseblends.

[0005] We believe that there is considerable potential for extending theuse of polymers by means of oxygen-scavenging systems. In these, oxygenreacts chemically as it is transmitted inwards towards the packagecontents. Accordingly, transmission of oxygen inwards to the packagecontents is reduced, not necessarily with any improvement in theperformance of the package with respect to inward transmission of othersubstances such as nitrogen or water vapour or outward transmission ofsubstances.

[0006] Among substances that we believe can then be more satisfactorilypackaged with polymers we would particularly mention beers (especiallylager beers), wines (especially white ones), fruit juices, somecarbonated soft drinks, fruits, nuts, vegetables, meat products, babyfoods, coffee, sauces, and dairy products. Almost all foods andbeverages are likely to display some benefit.

[0007] Oxygen-scavenging implies consumption of a material incorporatedin the wall of the package. This will be progressively consumed, so thatthe high barrier to oxygen must in principle be of limited duration.However, the deterioration of the barrier to oxygen is not necessarilycommercially very significant. An advantage is obtained so long as therate of such deterioration is not too great with respect to the time forwhich the deterioration can occur prior to consumption of the product.This will depend on the time from packaging to consumption and also onany relevant storage times of raw materials, fabricated packagingmaterials, and containers prior to their use in packaging the product.Good oxygen barrier performance over periods as short as one day mightbe in principle of use in certain cases, although periods of at leasttwo, five, ten, twenty, fifty, or hundred days will extend the range ofcommercial applications. In respect of the prospective advantage fromreducing barrier over short periods only, it should be remembered thatoxygen entering the package shortly after the product is packaged has alonger time to react and therefore do damage than oxygen entering at atime nearer to consumption. It should also be remembered that in somecases oxygen will be packed with the product so that improvement of theperformance of the package beyond a certain point may have a relativelyinsignificant effect on product quality.

[0008] An early proposal relating to oxygen-scavenging is described inU.S. Pat. No. 3,856,514 (published in 1971). This describes mostparticularly the addition of 0.8% to 2% by weight of antioxidants tohard polyvinyl chloride. Antioxidants exemplified are2,2′-methylene-bis-(4-methyl-6-t-butylphenol) and2,2′-dihydroxy-3,3′-dicyclohexyl-5,5′-dimethyldiphenylmethane. The bestpermeability value reported is twenty times lower than that of thepolyvinyl chloride without the antioxidant. Experimental evidence on theduration of the effect is not given.

[0009] U.S. Pat. No. 4,048,361 (published in 1977) describes amultilayer structure in which a barrier layer such as anacrylonitrile-containing polymer, a terephthalate polyester,polyvinylidene chloride, a cellulosic material, or an elastomer isadhered to a layer comprising a carrier such as a polyolefin,polystyrene, and polyvinyl chloride and an antioxidant. No quantitativeexperimental investigation of the barrier properties is described. Theuse of antioxidants with polyethylene terephthalate is not specificallydisclosed; in this respect it may be noted that antioxidants are notadded to polyethylene terephthalate conventionally. (The conventionaluse of antioxidants is the suppression of oxidation of polymers, suchoxidation in a package being regarded generally as undesirable.

[0010] More recently, Rooney has described scavenging systems whichoperate by oxidation of organic materials such as 1,3-diphenylbenzofuranwhen illuminated in the presence of a dyestuff (Chem. Ind., 1979,900-901; J. Food Science, 1981, 47, 291-298; Chem. Ind., 1982, 197-198).These systems have the disadvantage for use with, say, beer bottles thatit is not practical to arrange for each bottle to be illuminated duringstorage.

[0011] As well as these proposals to use organic materials as scavengersthere have been proposals to use inorganic reducing agents as follows:iron powder (Japanese published patent application 55 106519, publishedin 1980); hydrogen gas packed with the product (UK patent 1,188,170,published in 1970); and sulphites (UK patent specification 1,572,902,published 1980, and European published patent application 83 826published 1983). There has been some commercial application of inorganicreducing agents. However, special packing procedures are of coursenecessary if hydrogen is used, and the use of sulphites and of ironrequires special procedures for wall fabrication because of their poorcompatibility with polymers.

[0012] Some discussion of the conventional measurements and units ofoxygen permeation is appropriate at this point. The measurement is madeby exposing a package wall of area A to a partial pressure p of oxygenon the one side and to an essentially zero partial pressure of oxygen onthe other. The quantity of oxygen emerging on the latter side ismeasured and expressed as a volume rate dV/dt, the volume beingconverted to some standard conditions of temperature and pressure. Aftera certain time of exposure (usually a few days) dV/dt is generally foundto stabilise, and a P_(W) value is calculated from the equation (1).

dV/dt=P _(W) A p   (1)

[0013] P_(W) in the present specification and claims is called thepermeance of the wall. (Analogy with magnetic permeance and electricalconductance would suggest that P_(W) should be described as “permeanceper unit area”, but we are following the nomenclature in Encyclopaediaof Polymer Science and Technology, Vol. 2, Wiley Interscience, 1985,page 178.) The standard conditions for expressing dV/dt used generallyand in this specification are 0° C. and 1 atm (1 atm=101 325 N m⁻²). Ifthe thickness of the area of wall is substantially constant over thearea A with value T and the wall is uniform through the thickness (i.e.the wall is not a laminated or coated one) then the permeability of thematerial in the direction normal to the wall is calculated from theequation (2).

dV/dt=P _(M) A p/T   (2)

[0014] For non-scavenging materials, P_(W) and P_(M) are to a reasonableapproximation independent of t and p, and P_(M) of T although they areoften appreciably dependent on other conditions of the measurement suchas the humidity of the atmosphere on the oxygen-rich side and thetemperature of the measurement.

[0015] For oxygen-scavenging walls, P_(W) and P_(M) are functions of tbecause the concentrations and activity of scavenger vary with time(particularly as the scavenger is consumed). This has not prevented ususually from measuring P_(W) and P_(M) reasonably accurately as afunction of time (the changes in dV/dt being relatively gradual once thenormal initial equilibration period of a few days is over). However, itshould be recognised that, whereas after a few days' exposure to themeasurement conditions a non-scavenging wall achieves a steady state inwhich dV/dt is equal to the rate of oxygen ingress to the wall, ascavenging wall achieves an (almost) steady state in which dV/dt isconsiderably less than the rate of oxygen ingress to the wall. Thisbeing the case, it is likely that P_(W) calculated from (1) is afunction of p as well as of t and that P_(M) in (2) is a function of pand T as well as of t. P_(W) and P_(M) for scavenging walls are,strictly speaking, not true permeances and permeabilities at all (sincepermeation and scavenging are occurring simultaneously) but, rather,apparent one. However, we have chosen to retain the conventional terms“permeance” and “permeability”. So long as the conditions of themeasurement are sufficiently specified they are suitable forcharacterising the walls in a manner relevant to the packaging user(i.e. in terms of the oxygen emerging from the wall).

[0016] All values of P_(W) and P_(M) hereinafter in this specification(except where stated otherwise) are to be understood to refer toconditions in which p=0.21 atm, the relative humidity on the oxygen-richside of the wall is 50%, the temperature is 23° C. and (in the case ofP_(M) values) the thickness of the wall is 0.3 mm. Conditions close tothe first three of these, at least, are conventional in the packagingindustry.

[0017] Further, as will be appreciated from the above discussion of thepapers by Rooney, it is possible for P_(W) and P_(M) to be affected bythe illumination of the wall under test. All P_(W) and P_(M) valueshereinafter, and indeed all references to oxidation, oxidisability, andoxygen-scavenging properties, refer to the dark or else to conditions ofirradiation not appreciably contributing to oxygen-scavenging.

[0018] The present invention provides a wall for a package, which wallcomprises, or includes a layer comprising, a composition comprising apolymer and having oxygen-scavenging properties, characterised in thatthe composition scavenges oxygen through the metal-catalysed oxidationof an oxidisable organic component thereof.

[0019] It is important to note in respect of the above and the rest ofthe present specification and claims that the oxidisable organiccomponent may be an oxidisable polymer. The use of an oxidisable polymeras the oxidisable organic component has the advantage, broadly speaking,over the use of an oxidisable non-polymeric component that it is lesslikely to affect adversely the properties of a non-oxidisable polymerwith which it is blended. It is possible for an oxidisable polymer to beused as the sole polymer in the composition, serving a dual function aspolymer and oxidisable organic component.

[0020] It is to be noted in the same respect that it is of coursepossible for two or more polymers, two or more oxidisable organiccomponents, or two or more catalysts to be used. It is possible also fora metal catalyst to be used in combination with a non-metal catalyst.For instance, with some oxidisable organic components an organicperoxide may be used in combination with the metal catalyst.

[0021] By “wall for a package” in the present specification and claimsis included (except where the context indicates otherwise) not only awall when incorporated into a package structure but also packagingmaterials capable of forming walls, such as package bases, packagingsheet, and so on.

[0022] The word “catalyst” is used in the present specification andclaims in a general way readily understood by the man skilled in theart, not necessarily to imply that it is not consumed at all in theoxidation. It is indeed possible that the catalyst may be convertedcyclically from one state to another and back again as successivequantities of oxidisable component are consumed by successive quantitiesof oxygen. However, it may be that some is lost in side reactions,possibly contributing directly to oxygen-scavenging in small measure, orindeed that the “catalyst” is more properly described an an initiator(e.g. generating free radicals which through branching chain reactionslead to the scavenging of oxygen out of proportion to the quantity of“catalyst”).

[0023] Advantageously, the permeance of the wall, for oxygen, is notmore than 10.0 cm³/(m² atm day), preferably not more than 5.0 cm³/(m²atm day), more preferably not more than 2.0 cm³/(m² atm day), especiallynot more than 0.5 cm³/(m² atm day), and most especially not more than0.1 cm³/(m² atm day).

[0024] Advantageously, the permeance of the wall provided by the presentinvention is not more than three-quarters of that which it would have inthe absence of oxygen-scavenging properties, preferably not more thanone half, more preferably not more than one tenth, especially not morethan one twenty-fifth, and most especially not more than one hundredth.

[0025] Such a permeance should advantageously be maintained for at leastone day when the wall is exposed on both sides to air at 23° C. and 50%relative humidity, and more preferably for the longer periods referredto in the preliminary discussion above.

[0026] The necessary scavenging capacity of the wall will generally haveto be greater the greater is the permeance in the absence of scavengingproperties. Accordingly, a good effect even in relative terms is harderto achieve the higher is this latter permeance. Advantageously,therefore, the permeance in the absence of oxygen-scavenging propertiesis not more than 50 cm³/(m² atm day), preferably not more than 30cm³/(m² atm day), most preferably not more than 18.0 cm³/(m² atm day). Aparticularly good effect can be achieved where the said permeance is inthe range from 1.5, preferably 3.0, to 30, preferably 18.0, cm³/(m² atmday). While we believe that a good relative effect should be achievablewhen said permeances are lower than 1.5 cm³/(m² atm day), the range ofcommercial applications seems to us to be relatively limited (generallybecause this would involve using in the wall major quantities ofexisting high barrier polymers rather than very convenient polymers suchas polyethylene terephthalate).

[0027] The wall may be a rigid one, a flexible sheet, or a clingingfilm. It may be homogenous or a laminate or coated with other polymers.If it is laminated or coated, then the scavenging property may reside ina layer of the wall the permeance of which is relatively high in theabsence of scavenging and which alone would not perform verysatisfactorily but which performs satisfactorily in combination with oneor more other layers which have a relatively low permeance butnegligible or insufficient oxygen-scavenging properties. A single suchlayer could be used on the outside of the package since this is the sidefrom which oxygen primarily comes when the package is filled and sealed.However, such a layer to either side of the scavenging layer wouldreduce consumption of scavenging capacity prior to filling and sealing.

[0028] The present invention provides in its second aspect a compositionfor packaging use which comprises a polymer, an oxidisable organiccomponent, and a metal catalyst for the oxidation of the oxidisableorganic component.

[0029] The composition provided by the present invention has three majoruses.

[0030] Firstly, it can be used as the material for a wall (uniform inthe direction normal to the wall at least) or else a layer of a wallproviding the major part of the overall barrier. In such a case, thepermeability of the composition for oxygen is advantageously not morethan 3.0, preferably 1.7, more preferably 0.7, especially 0.2, and mostespecially 0.03 cm³ mm/(m² atm day). The permeability of the compositionprovided by the present invention is advantageously not more thanthree-quarters of that in the absence of oxygen-scavenging properties,preferably not more than one half, more preferably not more thanone-tenth, especially not more than one twenty-fifth, and mostespecially not more than one-hundredth. The permeability in the absenceof oxygen-scavenging properties is advantageously not more than 17 cm³mm/(m² atm day), preferably 10, and most preferably 6. A particularlygood effect can be achieved for such permeabilities in the range from0.5, preferably 1.0, to 10, preferably 6.0, cm³ mm/(m² atm day).

[0031] Secondly, the composition can be used as a master batch forblending with another polymer for such use.

[0032] Thirdly, it can be used for forming a layer of a wall whichprimarily provides oxygen-scavenging (another layer including polymerproviding gas barrier without significant scavenging), or as ahead-space scavenger (completely enclosed, together with the packagecontents, by a package wall).

[0033] The time period for which the permeability is maintained when thecomposition is stored in air, as granules or in another form, is notnecessarily critical since storage in sealed containers or undernitrogen is practical. However, preferably the permeability should bemaintained in air for the periods referred to above in respect of thewall provided by the invention. More importantly, however, thepermeability should preferably be maintained when a typical wall is made(0.3 mm thick).

[0034] In a third aspect, the invention provides a package, whetherrigid, semi-rigid, collapsible, lidded, or flexible or a combination ofthese, a wall of which is a wall as provided by the present invention inits first aspect or comprises entirely, as a layer, or as a blend thecomposition provided by the invention in its second aspect.

[0035] Before we proceed to describe the present invention in moredetail (including by means of Examples and an Experiment) it isappropriate to deal with the question of how one may determine permeanceor permeability that a wall or composition would have in the absence ofscavenging (this permeance or permeability being referred to severaltimes above). The ratio of permeances or permeabilities in the presenceand absence of scavenging are one (reciprocal) measure of the size ofthe scavenging effect, and it is for this reason that various upperlimits on this ratio are suggested above. (Another measure might be theratio of the quantities of oxygen emerging and entering the wall undertest, but this is less practically convenient.) Four methods ofdetermining the permeances or permeabilities in question will now bedescribed with particular reference to determining whether a particularpreferred ratio (¾, ½, {fraction (1/10)} etc. as described above) isexceeded:

[0036] (1) The wall under test is exposed to oxygen for a timesufficiently long that the oxygen permeance or permeability begins torise as the oxidisable organic component is consumed. It is of coursenot necessary to continue the exposure until no further rise occurs(i.e. until the scavenging is totally absent). Whenever the exposure isterminated for a particular sample one can confidently set a lower limiton permeance or permeability in the absence of scavenging, and thereforean upper limit on the ratio in question.

[0037] (2) A wall is prepared for comparison free of catalyst, and theeffect of the catalyst on pure permeation is estimated or (more likely)reasonably ignored. Some scavenging activity in the absence of catalystwill not preclude the establishment of the lower and upper limitsreferred to in (1).

[0038] (3) In some cases, as will be discussed in more detail later, theoxygen-scavenging property is still undeveloped until some time afterthe forming of a wall, in which case one may take the largest P_(W) orP_(M) value observed before achievement of maximum barrier as setting alower limit on P_(W) or P_(M) in the absence or scavenging (results onunequilibrated samples being ignored, of course).

[0039] (4) In some cases, the oxygen-scavenging effect can be suppressedby cooling the wall or composition. With due allowance for the effect ofchanged temperature, the lower and upper limits referred to in (1) canbe established.

[0040] Of the methods (1) to (4) above, (1) is probably the mostgeneral, although for very good materials the experimental time could bevery long (e.g. exceeding one year) unless accelerating conditions wereused (e.g. higher temperature, high partial pressures of oxygen). webelieve that the walls and compositions in accordance with the presentinvention should all display a plot of permeance or permeability againsttime of exposure to oxygen essentially as shown in FIG. 1 attachedhereto. However, it being relatively recently that this invention wasmade, we do not know the precise form of the whole curve. It should benoted that a similar curve for an inert gas such as nitrogen or carbondioxide is not to be expected, nor is such a curve to be expected fromknown materials of high barrier properties although a long term increaseof permeance or permeability both for oxygen and for nitrogen or carbondioxide might occur as a result of general degradation.

[0041] This indicates a possible fifth method of test, namely performingcomparative experiments with oxygen and an inert gas while making dueallowance for the difference of gas based on broadly similarconventional materials. The validity of this method in principle we haveconfirmed by our finding that bottles made in accordance with thepresent invention provide an unexceptional barrier to loss of carbondioxide from carbonated water contained in them.

[0042] The oxidisable component/metal catalyst combination to be used inaccordance with the present invention in all its aspects may be selectedby experimental trial and error such as the man skilled in the art mayreadily devise. A good preliminary screening can be achieved by means ofpure scavenging measurements on granulates (see Example 7 for a possibleprocedure). A metal catalyst that is highly effective for one oxidisableorganic component may be less effective for another. The effectivenessmay depend on the precise grade of the organic component or of thepolymer in the composition. It will depend on what fillers, conventionalantioxidants, catalyst residues from polymerisation, pigments and dyesmay be present or added.

[0043] We do not understand fully the role which the metal catalystplays in the oxidation, although we regard metals with at least twopositive oxidation states, especially transition metals, as the mostpromising catalysts when added in one of the positive oxidation states,particularly as cations. Thus cobalt added in the II and III state,rhodium added in the II state, and copper added in the II state haveproved effective with some oxidisable organic components. Addition inthe form of a carboxylate has proved convenient. Generally speaking,higher levels of catalyst achieve better scavenging. In the absence ofundesired interactions between the catalyst and the other components(such as depolymerisation) a weight fraction of metal relative to thetotal composition of up to 5000 ppm can be readily contemplated. We havefound that levels of at least 10, preferably 50, more preferably 100 ppmof metal can achieve catalysis (the precise level being determined bytrial and error for a particular overall composition). In wallapplications (as opposed to master batch applications where morecatalyst is used) we have preferred to keep the level of metal below300, more preferably 250 ppm.

[0044] In general, where the aim is to modify a non-oxidisable polymerso as to form a wall having scavenging properties the weight fraction ofthe oxidisable organic component is likely to lie in the range from 1 to7 percent. However, where the oxidisable organic component is itself apolymer, then it may, depending on compatibility, be used in blends overa wide range of relative proportions with a non-oxidisable polymer orindeed be used as the sole polymer component of the composition (i.e.weight fractions from 1 to 100 percent). Higher weight fractions may beespecially valuable with thin films and/or non-oxidisable polymers ofrelatively high permeability when high oxygen ingress rates areexpected. Particularly interesting oxidisable polymers are thepolyamides, especially those containing groups of the formula-arylene-CH₂—NH—CO—, conveniently in—NH—CH₂-arylene-CH₂—NH—CO-alkylene-CO— units. These polyamides are ofespecial interest with cobalt and rhodium catalysts. Especially suitablearylene groups are phenylene groups, particularly m-phenylene groups,which may be alkyl-substituted and/or condensed with other unsubstitutedor alkyl-substituted aromatic rings. Alkylene and alkyl groupsconveniently have from 1 to 10 carbon atoms and may be straight-chain orbranched. Especially suitable alkylene groups are n-butylene groups.MXD₆ is very suitable. Conveniently, the relative viscosity (also calledviscosity ratio) of polyamides containing —NH—CH₂—arylene-CH₂—NH—CO-alkylene-CO— groups lies in the range from 1.5 to 4.5,especially 2.0 to 3.6 (measured for solutions in 95% aqueous sulphuricacid containing 1 g of polymer per 100 cm³ solution).

[0045] Fully aliphatic polyamides are promising, comprising—CO(CH₂)_(n)CONH(CH₂)_(m)NH— or —(CH₂)_(p)CONH— units (n, m, and p beingintegers usually 4, 5, or 6), although we have so far not achieved thevery good results which we have achieved with MXD6. In general, thepolyamide may include polymer linkages, side-chains, and end groups notrelated to the formal precursors of a simple polyamide (i.e. compoundshaving at least two amino groups per molecule together with those havingat least two carboxylic acid groups per molecule, or aminocarboxylicacids). Conveniently, at least 90 mole percent of the polymer's formalprecursors will be such. However, a polymer including a minority ofamide linkages would in principle work, such a polymer perhaps beingused as the sole polymeric component of the composition. Even in such acase, however, one would expect to include in the composition aconcentration of —CONH— linkages similar to that which one would usewith MXD6—i.e. concentrations of —CONH— in the total composition of atleast 0.08 mmol/g, most commonly up to 0.6 mmol/g.

[0046] From a purely chemical standpoint, non-polymeric amides areattractive as oxidisable organic components. Non-polymeric compoundscontaining a group or groups of the formula-alkylene-CO—NH—CH₂-1,3-phenylene-CH₂—NH—CO— alkylene- are of interest,especially with cobalt and rhodium catalysts. The above comments onalkylene and 1,3-phenylene groups, made with reference to polymericamides, apply here except that n-butylene is not so convenient if analkylene group is terminated by H. An example of such a non-polymericcompound is n-C₃H₇—CO—NH—CH₂-m-C₆H₄—CH₂—NH—CO-n-C₃H₇, which in thepresence of cobalt we have found to scavenge oxygen well, although itssuitability for use in accordance with the present invention needs ofcourse to be determined by trial and error in a particular application.

[0047] Other non-polymeric oxidisable compounds are also of interest,for instance conventional antioxidants including substituted phenols,especially 2,4,6-tri-(t-butyl)phenol.

[0048] Subject to the above preferences on physical properties,non-oxidisable polymers used according to the present invention in allits aspects can be chosen with fair freedom, unless there is somespecific inhibition of the scavenging system or other untowardinteraction. In principle, there may be a favourable interaction (e.g.if the non-oxidisable polymer contains as catalyst residues metalscatalysing the oxidation of the oxidisable organic component); but incurrent commercial products the levels are usually low and the catalystmay be at least partially poisoned by the other residues or additives.

[0049] Polymers (formally) of one or more phthalic acids with one ormore organic compounds containing at least two alcoholic hydroxy groupsper molecule can offer fair impermeability in the absence of scavenging.Preferably, the permeabilities should be less than 6.0 cm³ mm/(m² atmday). Phthalic acid polyesters based on terephthalic or isophthaiic acidare commercially available and convenient; the hydroxy compounds aretypically ethylene glycol (which may yield diethylene glycol units insitu), and 1,4-di-(hydroxymethyl)-cyclohexene. Conveniently, theintrinsic viscosity (also called limiting viscosity number) for aphthalic acid polyester lies in the range from 0.6 to 1.2, especially0.7 to 1.0 (for o-chlorophenol solvent). 0.6 corresponds approximatelyto a viscosity average molecular weight of 59 000, and 1.2 to 112 000.

[0050] In general, the phthalate polyester may include polymer linkages,side chains, and end groups not related to the formal precursors of asimple phthalate polyester previously specified. Conveniently, at least90 mole percent will be terephthalic acid and at least 45 mole percentan aliphatic glycol or glycols, especially ethylene glycol.

[0051] Polyolefins blended with a scavenging system have been found towork, and by lamination or coating with less permeable material walls ofinteresting overall barrier properties should be achievable.

[0052] The composition may, as previously mentioned, include othercomponents such as pigments, fillers, and dyestuffs. Usually, the totalquantity of such components will be less than 10%, more usually lessthan 5%, by weight relative to the whole composition.

[0053] Compositions which we think may be of especial importance on thebasis of our experiments to date include the following (the percentagesbeing the weight fractions relative to the total composition):

[0054] compositions comprising at least 90%, preferably 95%, ofpolyethylene terephthalate and/or a polyamide taken together and havinga permeability to oxygen of not more than 0.01 cm³ mm/(m² atm day);

[0055] compositions containing at least 90% of polyethyleneterephthalate, preferably 95%, and having a permeability to oxygen ofnot more than 0.3 cm³ mm/m² atm day), and preferably not more than 0.1cm³ mm/(m² atm day), and more preferably not more than 0.03 cm³ mm/(m²atm day), preferably at least 0.5%, more preferably 1%, and alsopreferably less than 7% of the composition consisting of a polyamide;and

[0056] compositions comprising at least 90%, preferably 95%, of apolyamide and having a permeability to oxygen of not more than 0.01 cm³mm/(m² atm day).

[0057] The composition provided by the present invention or used inwalls provided by the present invention is preferably formed by mixingthe metal catalyst with the other component or components of thecomposition all together or in any sequence. The metal catalyst ispreferably added in the form of a solution or slurry. Conveniently, themixing includes or is followed by melt-blending at a temperatureappropriate to the components, commonly in the range from 100° C. to300° C. The blending may immediately precede the formation of thefinished article or a preform or parison, or may be followed byformation of feedstock for later use in the production of the finishedarticle. We have found additions of catalyst in the range of 10 to 250,especially 50 to 200, ppm to be convenient.

[0058] The oxidation catalyst may be added to the monomers from whichone or more polymeric components of a composition are made, rather thanbeing added as proposed above in a subsequent blending step. Clearly, ifthe oxidation catalyst neither interferes with nor is affected by thepolymerisation process then this may be an attractive option. If thecatalyst interferes or assists with the polymerisation or is at leastpartially poisoned by the usual steps in the polymerisation (as may bethe case with cobalt and polyethylene terephthalate production), thenmodification or careful selection of polymerisation protocols will benecessary.

[0059] In some systems at least, the scavenging properties do not emergeimmediately after the blending, but only after ageing. This may bebecause catalyst species have to migrate to relevant sites in thecomposition because it is incorporated so as to be present in the“wrong” phase or because the relevant sites in the oxidisable componentto which they were attached during processing were very largely oxidisedduring processing, or because a slow initiation is involved, or for someother reason. Prolonged ageing at ordinary temperatures, or ageingaccelerated by elevated temperatures, are in principle possible but arecostly. However, the higher the level of catalyst used, generally theless ageing is required. Indeed, we have achieved very high barrier tooxygen so soon after fabrication of walls that any delay is comparablewith or shorter than the normal time required to equilibrate the wall onthe OXTRAN machine, and is unlikely to impose significant costpenalties. In general, one would seek to achieve high barrier within 30days, preferably 20 days, and more preferably 10 days, of the wall beingfabricated if the wall is stored at 23° C. and 50% relative humidity.

[0060] We shall now consider briefly the packaging structures andforming techniques that will be appropriate when the present inventionis used for packaging. Where the oxidisable organic component isnon-polymeric it may have a significant effect on the forming techniquesused, especially on the temperatures that may be used if the componentis volatile. This in turn will affect the structures that can readily bemade. Where, however, the composition used comprises oxidisable polymerplus catalyst, or non-oxidisable polymer, oxidisable polymer, pluscatalyst, then the forming techniques and structures can be expected tomatch those appropriate to the oxidisable polymer or its blend in theabsence of catalyst; the quantities of catalyst used are likely to betoo small to have much effect on mechanical properties in most cases.

[0061] Among the techniques that may be in question are mouldinggenerally, injection moulding, stretch blow moulding, extrusion,thermoforming, extrusion blow moulding, and (specifically for multilayerstructures) co-extrusion and lamination using adhesive tie layers.Orientation, e.g. by stretch blow moulding, of the polymer is especiallyattractive with phthalate polyesters and their blends with MXD6 becauseof the known mechanical and (in the latter case) barrier advantages thatresult.

[0062] In the discussion of wall structures according to the inventionearly in this specification, the design considerations relating to thebarrier properties were referred to. However, there are more generalconsiderations, familiar in the art, which will be taken into account inpractical applications.

[0063] One such consideration is rigidity. If a plastic container is tobe self-supporting when empty, then the thickness of the wall is likelyto lie in the range from 200 to 500 micrometer; such containers areoften referred to as “semi-rigid”. More flexible packaging structuressuch as meat packs are likely to have wall thickness in the range from20 to 200 micrometer. Where thick structures are required, one maychoose to provide only a thin highly effective scavenging barrier layersupported by mechanically superior or cheaper relatively poor barriers.

[0064] Another consideration is the requirements for bonding of the wallmade in accordance with the present invention. For instance, an extralayer may be added to a sheet so as to permit heat sealing to complete apackage structure.

[0065] A further consideration is the protection of theoxygen-scavenging composition from the package contents or theenvironment if direct contact causes any difficulties (e.g. undesirablechemical reactions or leaching). In such a case a protective layer willbe provided on the appropriate side of the layer containing theoxygen-scavenging composition.

[0066] For the avoidance of any possible doubt resulting from the twosets of design considerations for multilayer structures, three suchstructures for walls according to the present invention will now bedescribed, by way of illustration only, by reference to the FIGS. 3 to5, each representing schematic sections (not to scale) of multilayerwalls according to the invention.

[0067] In FIG. 3, layer 1 consists of a blend of a first polymer, anoxidisable organic component, and a metal catalyst. Layers 2 and 3consist of a second polymer having a permeability much less than thepermeability of the pure first polymer. The overall permeanceperformance of the wall is markedly superior to that of a single-layerwall of the same composition as layers 2 and 3 or of a single-layer wallof the same composition as layer 1.

[0068] In FIG. 4, layer 1 consists of an oxidisable polymer and a metalcatalyst and alone would have a low permeance. Layer 1 is too thin forthe proposed use and is supported by layers 2 and 3 of a non-oxidisablepolymer which do not significantly reduce the permeance.

[0069] In FIG. 5, layer 1 consists of a blend of a first polymer, andoxidisable organic component, and a metal catalyst. Its permeance is lowand it could be economically used at a thickness appropriate to theproposed use. However, layer 1 is protected from undesired directinteraction with the package contents and the environment by layers 2and 3 of a second polymer which do not significantly reduce thepermeance.

[0070] The present invention will now be further described, by way ofillustration only, by means of the following Examples and an Experiment.

EXAMPLES 1 to 5

[0071] The materials used in these Examples were of the grades specifiedbelow. Further information was obtained by our own measurements or fromthe manufacturers' literature.

[0072] Polyethylene terephthalate, grade B90N, from ICI of UK. This is apolymer of ethylene glycol with terephthalic acid. It was found tocontain 35 ppm cobalt, 25 ppm sodium, 38 ppm phosphorus, and 32 ppmantimony, with ≦1 ppm of copper, germanium, iron, manganese, andtitanium. The intrinsic viscosity in Q-chlorophenol is 0.82.

[0073] MXD6, grade Renv 6001, from Mitsubishi Gas Chemicals of Japan.This is a polymer of meta-xylylenediamine H₂NCH₂-m-C₆H₄—CH₂NH₂ withadipic acid HO₂C(CH₂)₄CO₂H. The relative viscosity of the polyamide is2.1, for a solution in 95% aqueous sulphuric acid containing 1 g ofpolymer per 100 cm³ of solution.

[0074] Cobalt Siccatol, from Akzo Chemie (“Siccatol” is a trade mark).This is a solution in white spirit of C₈-C₁₀ cobalt carboxylates. Theconcentration of cobalt (as metal) is 10% by weight relative to thesolution.

[0075] Granules of the polyethylene terephthalate and of the MXD6 weremixed by hand in a tray together with the Siccatol solution in therelevant proportions. The mixture was then heated at 100° C. for 18hours in a recirulating dehumidified air dryer (this to remove waterfrom the two polymers so as to avoid degradation in injection moulding,as well as incidentally driving off unevaporated white spirit).

[0076] The mixture was then used to make a preform for a one-litercylindrical bottle. The injection moulding was performed on a KraussMaffei KM 150 machine. The mass of the preform was approximately 33 g.The preform was then reheated and blown to form the bottle with biaxialorientation (i.e. circumferential and longitudinal orientation). Forthis, a Corpoplast BMB3 stretch blow moulding machine was used. Thebottle had a wall thickness of 0.3 mm.

[0077] Five bottles were made and tested for oxygen permeance on anOXTRAN machine 10/50 A made by Mocon Inc of USA. The conditions of thetests were as set out earlier in this specification.

[0078] Tests were performed at various times after the bottle had beenmanufactured. In between tests, the bottles were stored with air bothinside and out. Each test lasts 3 to 4 days until the bottle (as isusual) “equilibrates” from its storage conditions (exposed to theatmosphere inside and out) to the test conditions.

[0079] The various compositions and the test results obtained are setout in Tables 1 and 2. The permeances per unit area quoted arecalculated from the OXTRAN result on the basis of an oxygen partialpressure of 0.21 atm and a bottle area of 0.0575 m². P_(W)=O indicatesthat no oxygen transmission was detected. The bottle wall beingessentially uniform, they may be converted into permeabilities in cm³mm/(m² atm day) for the material by multiplying them by 0.3.

[0080] For comparison, in Table 2, are also listed the P_(W) valuesobserved (or calculated from reported P_(M) values) for similar bottlesmade from the same polymer components in which the oxygen-scavengingeffect is absent (no addition of cobalt). These figures are approximate,but the spectacular character of the effect is immediately evident fromthe comparison.

[0081] The results of Examples 1 and 3 are plotted in FIG. 2.

[0082] A rough calculation for Example 3 based on the comparison P_(W)figure indicates that at the time of the last measurement the bottlewill have scavenged at least 0.9 mmol of 0₂. The bottle contains only0.11 mmol of Co, establishing that the cobalt functions as a catalyst inthe sense previously described.

[0083] The Examples show that, notwithstanding some variability betweensamples of similar composition, there is a broad positive correlationbetween the extent and duration of scavenging and the levels of both theoxidisable organic component and the catalyst. TABLE 1 WEIGHT FRACTIONSOF RAW MATERIALS USED RELATIVE TO TIME IN TOTAL BALANCE DAYS FROMPOLYETHYLENE MANU- TEREPHTHALATE FACTURE WEIGHT OF FIRST WEIGHT FRACTIONSTORAGE MEASURE- EXAMPLE FRACTION COBALT CONDI- MENT No. MXD6 AS METALTION P_(W) = 0 1 4%  50 ppm 23° C. 10 50% R.H. 2 4%  50 ppm Uncontrolled 3 storage cooler than 1 3 4% 200 ppm as 1  3 4 2%  50 ppm as 2 10 5 1% 50 ppm as 2 20

[0084] TABLE 2 This table gives P_(W) at time t after first measurementof P_(W) = O and a comparison P_(W) (no scavenging) for Examples 1 to 5.EXAMPLE 1 test results t 0 24 57 105 150 203 270 in day P_(W) in 0 00.016 0.19 0.6 0.8 1.2 cm³ {overscore ((m² atm day))} EXAMPLE 2 testresults t 0 135 192 207 in day P_(W) in 0 0.025 0.3 0.35 cm³ {overscore((m² atm day))} EXAMPLE 3 test results t 0 31 64 112 157 210 277 in dayP_(W) in 0 0 0.009 0 0.03 0.02 0.02 cm³ {overscore ((m² atm day))}EXAMPLE 4 test results t 0 125 185 200 in day P_(W) in 0 0.95 1.3 1.4cm³ {overscore ((m² atm day))} EXAMPLE 5 test results t 0 115 175 195 inday P_(W) in 0 2.7 3.1 3.3 cm³ {overscore ((m² atm day))}

EXAMPLE 6

[0085] This Example illustrates the use of a master batch.

[0086] MXD6 and Cobalt Siccatol were mixed and injection moulded intopreforms. 2000 ppm cobalt as metal was used by weight relative to theMXD6.

[0087] The preform was then granulated to make a master batch ofgranules. These were then mixed with polyethylene terephthalate to makefurther preforms, and these were blown into bottles the same day. 6% byweight of master batch and 94% by weight of polyethylene terephthalatewere used.

[0088] The procedures were as described in Examples 1 to 6 save that, ofcourse, polyethylene terephthalate was omitted in the first stage of theabove procedure and Cobalt Siccatol in the second.

[0089] The bottles achieved a P_(W) of 0.002 cm³/(m² atm day) within 2days.

EXAMPLE 7

[0090] This Example directly illustrates the scavenging properties ofcompositions in accordance with the invention, and the dependence of theproperties on temperature.

[0091] A preform was made as described in Examples 1 to 5 with the sameingredients, but the weight fractions of MXD6 and cobalt (on the samebasis) were 2% and 100 ppm respectively.

[0092] The preform was granulated and 25 g samples were sealed into eachof three 60 cm³ vials having a septum through which the head space gascould be sampled. The three vials (1 to 3 below) were stored atdifferent temperatures for 38 days and the head space gas was analysed.For comparison similar samples without the added cobalt were storedunder similar conditions (vials C1 to C3 below) and the head space gasanalysed. The results are summarised in the following table. The 0₂:N₂ratios are more reliably determined than the absolute values (themselvesnormalised so as to sum to 99%). Storage Volume fraction Volume fractionVial temperature of O₂ after of N₂ after No. in ° C. 38 days 38 days 1 4° C. 12 87 C1  4° C. 20 79 2 20° C.  8 91 C2 20° C. 20 79 3 55° C.  594 C3 55° C. 20 79

[0093] It will be seen that although the scavenging effect is reduced at4° C., it is still very appreciable, which is of course relevant topackaging applications where prolonged refrigerated or other coolstorage may occur.

[0094] A rough calculation for test vial 2 indicates that the amount ofO₂ scavenged over 38 days was 0.24 mmol, whereas the amount of thesample contained only 0.04 mmol Co, establishing again that the cobaltfunctions as a catalyst in the sense previously described.

EXAMPLE 8

[0095] This Example illustrates the present invention under testconditions, more closely approaching the actual (aqueous) conditions inbeverage applications. A nominal one-liter bottle was made as describedfor Examples 1 to 5, and with the same composition as the bottle ofExample 3.

[0096] The bottle had a volume of 1040 cm³ and was filled with 1000 cm³of water through which nitrogen gas was bubbled before the bottle wasfinally sealed with a septum permitting head space sampling.

[0097] The volume fraction of oxygen in the head space gas was monitoredas a function of time, the bottle being stored in ambient laboratoryconditions.

[0098] The volume fraction was less than 0.2% after 31 days, a verysimilar result being obtained with a glass bottle comparison. Acomparison bottle without the added cobalt gave a result of 1.1%.

[0099] The bottles were then subjected to a variety of temperatureconditions (a period at 38° C., 4° C., and ambient) and after 108 daysthe results for the example, the glass comparison, and the comparisonwithout added cobalt were 0.2%, 0.2%, and 2.7%.

EXAMPLE 9

[0100] This Example illustrates the use of a rhodium catalyst instead ofa cobalt catalyst in a system otherwise similar to those of Examples 1to 8.

[0101] Polyethylene terephthalate, MXD6, and a solution of rhodium (II)acetate dimer were mixed and dried overnight at 100° C. The first twocomponents were of the grades used in Examples 1 to 5. The weightfractions of MXD6 and of rhodium (as metal) relative to the wholemixture were 4% and 175 ppm respectively.

[0102] A preform for a 296 cm³ bottle was made on a Meiki 200 injectionmoulding machine, and the bottle was blown. Limit-of-detection oxygentransmission was observed on the OXTRAN machine previously referred to.

EXAMPLE 10

[0103] This Example illustrates the present invention applied to apolymer other than polyethylene terephthalate. It also demonstrates thescavenging in an injection-moulded (unblown) container.

[0104] Polypropylene (Solvay grade KL 104) straight from the bag wasmixed with MXD6 of the grade used in Examples 1 to 5 which had beenpreviously dried overnight at 100° C. in a dehumidifying air dryer andwith cobalt Siccatol. Without further drying, the mixture wasinjection-moulded to form a cylindrical pot on a Meiki 200 injectionmoulding machine. The pot had a wall thickness of 1.5 mm, was 61 mmdiameter, 70 mm high, and had a surface area of 0.015 m²

[0105] The weight fractions of MXD6 and cobalt (as metal) relative tothe whole composition were respectively 10% and 200 ppm. Permeances onthe OXTRAN machine of less than 16 cm³/(m² atm day) were observed over18 days of testing. A comparison without added cobalt had a permeance of26 cm³/(m² atm day).

[0106] This performance indicates a very high rate of scavenging andimplies that the composition may be useful for head space scavenging oras the scavenging layer in a wall including additionally anon-scavenging layer of low permeability.

EXAMPLE 11

[0107] This Example illustrates the use of a different scavenging systemonce more with polypropylene in place of polyethylene terephthalate.

[0108] Example 10 was repeated but instead of MXD6, nylon-6,6 of ICIgrade A100 pre-dried as supplied was used. Instead of Cobalt Siccatol, asolution of copper (II) acetate in methanol was used (7 g/dm³concentration). The weight fractions of nylon-6,6 and copper (as metal)relative to the total composition were 20% and 25 ppm respectively, thebalance being polypropylene.

[0109] Pink-coloured bottles were produced which had a permeance ofapproximately 6 cm³/(m² atm day) for 22 days of testing in the OXTRANmachine. A comparison bottle without added copper had a permeance of 9cm³/(m² atm day).

EXAMPLE 12

[0110] This Example illustrates another scavenging system with anothernon-oxidisable polymer. The metal catalyst in this case is assisted byan non-metallic catalyst, and the oxidisable organic component isnon-polymeric.

[0111] The procedure of Example 10 was repeated, but on this occasionwith low density polyethylene instead of polypropylene, and2,4,6-tri-(t-butyl)phenol and 2,5-dimethylhexane-2,5-di-(-t-butyl)peroxide instead of MXD6. The polyethylene was DSM grade Stanylan LD2308A; the substituted phenol was the material of Aldrich Chemical Co.Ltd; and the peroxide was the material of Interox Chemicals Ltd.

[0112] The weight fractions relative to the total composition were 4%substituted phenol, 1% peroxide, 100 ppm cobalt (as metal), and balancelow density polyethylene.

[0113] The permeance was consistently measured as 30-33 cm³/(m² atm day)over a period of 8 days, whereas a comparison without the added cobalthad values rising monotonically from its lowest value of 46 cm³/(m² atmday) to 66 cm³/(m² atm day) over the same period.

EXAMPLES 13 to 20

[0114] It is believed that the foregoing examples provide ampleinstruction to the man skilled in the art to put the present inventioninto effect, but for the sake of completeness there are listed in Table3 various other compositions we have found to perform well (permeancesless than 0.05 cm³/(m² atm day). The permeances were measured on 0.3 mmwalls except in the case of Example 18, where the wall was 1.5 mm thick.TABLE 3 Oxidisable Polymer organic Example (balance of component andCatalyst and No. composition) weight fraction weight fraction 13 PETMXD6 Co 100 ppm  4% added as Co (II) acetylacetonate 14 PET MXD6 Co 100ppm  4% added as Co (III) acetylacetonate 15 PET MXD6 Co 100 ppm  4%added as Co (II) stearate 16 PET MXD6 Co 100 ppm  4% added as DurhamChemicals Nuosvn 17 PET MXD6 Co 100 ppm  4% added as Co (II)neodecanoate 18 PETG MXD6 Co 200 ppm  5% added as Cobalt Siccatol 19P121 MXD6 Co 100 ppm  5% added as Cobalt Siccatol 20 — MXD6 Co 200 ppm100% added as Cobalt Siccatol

EXPERIMENT

[0115] Fibres of a material having the same composition as the masterbatch in Example 6 were formed into a film and the infra-red absorptionspectrum was observed. An absorption was observed at 1640 cm⁻¹ which webelieve represents an amide carbonyl absorption.

[0116] The material was then held in air in an oven at 55° C. for twomonths and the spectrum was once more observed. A new albeit relativelysmall peak was observed at 1740 cm⁻¹ which we believe represents acarbonyl absorption distinct from the amide carbonyl absorption at 1640cm⁻¹ (still present).

[0117] The same effect was observed after holding fibres at 100° C. inair for only 5 days.

[0118] No such effect was observed when MXD6 fibres without cobalt washeld in air at 100° C. for 5 days.

[0119] We believe that the new band may indicate a carbonyl group formedwhen the material scavenges oxygen, or possibly the carbonyl group inthe original material whose chemical environment has been changed byoxidation.

1. A wall for a package, which wall comprises, or includes a layercomprising, a composition comprising a polymer and havingoxygen-scavenging properties, characterised in that the compositionscavenges oxygen through the metal-catalysed oxidation of an oxidisableorganic component thereof.
 2. A wall according to claim 1, of which thepermeance, for oxygen, is not more than 10.0 cm³/(m² atm day).
 3. A wallaccording to claim 1, of which the permeance, for oxygen, is not morethan 2.0 cm³/(m² atm day).
 4. A wall according to claim 1, of which thepermeance, for oxygen, is not more than 0.5 cm³/(m² atm day).
 5. A wallaccording to any one of claims 1 to 4, of which the permeance, foroxygen, is not more than three-quarters of that which it would have inthe absence of oxygen-scavenging properties.
 6. A wall according to anyone of claims 1 to 4, of which the permeance, for oxygen, is not morethan {fraction (1/25)} of that which it would have in the absence ofoxygen-scavenging properties.
 7. A wall according to any one of claims 2to 6, of which the said permeance is maintainable at or below hespecified limit at 23° C. and 50% relative humidity for at least 20days.
 8. A wall according to any one of claims 2 to 6, of which the saidpermeance is maintainable below the specified limit at 23° C. and 50%relative humidity for at least 100 days.
 9. A wall according to anypreceding claim, which would have in the absence of oxygen-scavengingproperties a permeance of not more than 50 cm³/(m² atm day).
 10. A wallaccording to any one of claims 1 to 9, wherein the oxidisable organiccomponent is an oxidisable polymer.
 11. A wall according to any ofclaims 1 to 9, wherein the oxidisable organic component is a polyamide.12. A wall according to any of claims 1 to 9, wherein the oxidisableorganic component is a polymer containing units of the formula—NH—CH₂-arylene-CH₂—NH—CO-alkylene-CO—.
 13. A wall according to any oneof claims 1 to 12, wherein the metal catalyst is a cobalt compound. 14.A wall according to any one of claims 1 to 12, wherein the metalcatalyst is a rhodium compound.
 15. A wall according to any one ofclaims 1 to 12, wherein the metal catalyst is a copper compound.
 16. Awall according to any of claims 1 to 15, wherein the compositioncontains the metal catalyst in a weight fraction, expressed as metalrelative to the composition, in the range from 10 to 300 ppm.
 17. A wallaccording to any of claims 1 to 15, wherein the composition contains themetal catalyst in a weight fraction, expressed as metal relative to thecomposition, in the range from 100 to 250 ppm.
 18. A wall according toany one of claims 1 to 17, wherein the polymer is formally acondensation polymer of one or more phthalic acids with one or morecompounds containing at least two alcoholic hydroxy groups per molecule.19. A wall according to any one of claims 1 to 17, wherein the polymeris formally a condensation polymer of terephthalic acid with ethyleneglycol.
 20. A wall according to any one of claims 1 to 17, wherein thepolymer is a polyolefin.
 21. A wall according claim 20 wherein thepolyolefin is polypropylene or polyethylene.
 22. A wall according to anyof claims 1 to 17, wherein the oxidisable organic component and thepolymer are a single oxidisable polymer.
 23. A wall according to anypreceding claim, which comprises at least two layers, the first of whichcomprises the composition specified in claim 1 and the other or othersof which comprise a composition comprising a polymer and reduce by afactor of two or more the permeance that the wall would have in theabsence of oxygen-scavenging properties.
 24. A wall according to anypreceding claim, comprising at least two layers, the first of whichcomprises the composition specified in claim 1 and the other or othersof which afford mechanical stability or separation of the compositionfrom the environment or the package contents.
 25. A composition forpackaging use, which comprises a polymer, an oxidisable organiccomponent, and a metal catalyst for the oxidation of the oxidisableorganic component.
 26. A composition according to claim 25, of which thepermeability, for oxygen, is not more than 3.0 cm³ mm/(m² atm day). 27.A composition according to claim 25, of which the permeability, foroxygen, is not more than 0.7 cm³ mm/(m² atm day).
 28. A compositionaccording to claim 25, of which the permeability, for oxygen, is notmore than 0.2 cm³ mm/(m² atm day).
 29. A composition according to any ofclaims 25 to 28, which has a permeability not more than three-quartersof that which it would have in the absence of oxygen-scavengingproperties.
 30. A composition according to any of claims 26 to 29, ofwhich the said permeability is maintainable at or below the specifiedlimit at 23° C. and 50% relative humidity for at least 20 days.
 31. Acomposition according to any of claims 25 to 30, which would have apermeability in the absence of oxygen-scavenging properties of not morethan 17 cm³ mm/(m² atm day).
 32. A composition according to any ofclaims 25 to 31, having any of the features specified in any one ofclaims 10 to 22, for the wall according to claim
 1. 33. A method ofmaking a wall according to any one of claims 1 to 24, wherein thecomposition specified in claim 1 is prepared by mixing the metalcatalyst with the other component or components all together or in anyorder and the wall, or the layer of the wall, is formed from thecomposition so obtained.
 34. A method of making a composition accordingto any one of claims 25 to 32, which comprises mixing the metal catalystwith the other component or components all together or in any order. 35.A wall for a package, which wall comprises, or includes a layercomprising, a composition comprising a polymer and havingoxygen-scavenging properties, wherein the wall has a permeance of notmore than 2.0 cm³/(m² atm day) and would have in the absence ofoxygen-scavenging properties a permeance not exceeding 50 cm³/(m² atmday), characterised in that the composition scavenges oxygen through themetal-catalysed oxidation of an oxidisable organic polymer therein. 36.A package comprising a wall according to any one of claims 1 to 24 and35, or a wall made by the method according to claim
 33. 37. A beveragebottle comprising a wall according to any one of claims 1 to 24 and 35,or a wall made by the method according to claim
 33. 38. A food containercomprising a wall according to any one of claims 1 to 24 and 35, or awall made by the method according to claim 33.